A disk drive is a device implementing disk storage in which data are digitally recorded by various electronic, magnetic, optical or mechanical methods on disks (also referred to as the media). Disk storage is used in both computer storage and consumer electronic storage (e.g., audio CDs and video disks, standard DVD and Blu-Ray). To that end, disk drives may implement such disk storage with fixed or removable media. With removable media the device is usually distinguished from the media as in a compact disk drive and a compact disk. Notable types of disk drives are the hard disk drive (HDD) containing a nonremovable disk, the floppy disk drive (FDD) and its removable floppy disk, and various optical disk drives and associated optical disk media.
A hard disk drive stores data onto tracks, heads, and sectors of a disk. A sector is a segment of a track, and the track is a circle of recorded data on a single recording surface of a platter (an individual recording disk). The sector unit is the smallest size of data to be stored in a hard disk drive, and each file may have many sector units assigned to it. Digital disk drives are block storage devices. Each disk is divided into logical blocks (which may be larger or smaller than a physical sector). Blocks are addressed using their logical block addresses (LBA). Reading from or writing to disk happens at the granularity of blocks.
The disk drive interface is the mechanism/protocol of communication between the rest of the system and the disk drive itself. Storage devices intended for desktop and mobile computers typically use ATA (parallel ATA) and SATA (serial ATA) interfaces. Enterprise systems and other storage devices typically use SCSI (Simple Computer System Interface), SAS (serial attached SCSI), and FC (Fiber Channel) interfaces in addition to some use of SATA.
SCSI is popular on servers and high-performance workstations. RAID (Redundant Arrays of Independent Disks) servers also often use SCSI hard disks.